The invention relates to a driving circuit for light-emitting diodes which can be used to set the brightness of the light-emitting diodes. Light-emitting diodes are also used for showing information. In this case, either particular items of information are assigned particular light-emitting diodes, or else the displays are divided into a plurality of segments or matrices, each containing one or more light-emitting diodes. In this way, different items of information can be shown on a display according to whether the light-emitting diodes are switched on or off.
To drive the light-emitting diodes, it is known practice to impress the current through the light-emitting diodes using a series resistor connected between the driving voltage and the light-emitting diodes. Nevertheless, different forward voltages U.sub.LED of the individual light-emitting diodes (e.g. U.sub.LED =1.8 V to 2.5 V for red light-emitting diodes) mean different sizes of current through the light-emitting diodes and hence different brightnesses as well.
It is also known practice to drive the light-emitting diodes using a current source. In this way, forward-voltage tolerances of the light-emitting diodes and voltage-supply tolerances now have only a small influence on the brightness of the light-emitting diodes.
Finally, it is known practice to arrange a plurality of current sources in an integrated circuit. To keep the power loss in the integrated circuit to a level which prevents the integrated circuit from being destroyed as a result of thermal overstressing, known driving circuits involve the use of a series resistor for each current source, some of the superfluous voltage dropping across said series resistor and thus preventing the integrated circuits from overheating.
A disadvantage of this is that a relatively large number of series resistors are required for the known driving circuit.